To run a test payment, you will have to utilize an alternate Paypal/payment processor account separate from the account used to collect product sales. If you try to purchase using the same account that your product is set up under, you will receive an error.
The best way to run a test without errors is to use a friend or partner's account.
You will also want to ensure that your account is setup to take US Dollars, the default payment option. You can find out how to set your account up by reading this knowledge base article: